Current trends shaping the global energy landscape suggest an expanding utilization of low temperature heat (i.e. heat at temperatures lower than about 250° C.) in the near future. Such heat may be recovered from various commercial or industrial operations, can be extracted from geothermal or hydrothermal reservoirs or can be generated through solar collectors. Motivation for low temperature heat utilization is provided by increasing energy prices and a growing awareness of the environmental impacts, in general, and the threat to the earth's climate, in particular, from the use of fossil fuels.
Elevation of the temperature of available heat through high temperature mechanical compression heat pumps (HTHPs) to meet heating requirements is one promising approach for the use of low temperature heat. Heat pumps operating according to a reverse Rankine cycle require the use of working fluids. Commercially available working fluids that are used or could be used for HTHPs (e.g. HFC-245fa, Vertrel® XF, HFC-365mfc) are coming under increasing scrutiny because of their relatively high Global Warming Potential (GWP). Clearly, there is an increasing need for more environmentally sustainable working fluids for HTHPs.
The use of zero-ODP, low GWP working fluids based on hydrofluoroolefins (HFOs) for high temperature heat pumps has been previously disclosed. However, the critical temperatures of previously disclosed HFO-based working fluids limit the maximum practical condensing temperatures that could be delivered by a heat pump operating according to the conventional reverse Rankine cycle to about 160° C.
The compositions of the present invention are part of a continued search for the next generation of low global warming potential materials. Such materials must have low environmental impact, as measured by low global warming potential and zero ozone depletion potential. New heat pump and high temperature heat pump working fluids are needed.